Subcaliber adapter for firearm

ABSTRACT

A chamber insert which defines a small caliber chamber through which an undersized or subcaliber projectile can be fired. The defined chamber is eccentric with respect to the larger chamber and barrel of the large caliber firearm so as to enable a center fire large caliber firearm to fire a smaller rim fire subcaliber projectile. The eccentricity of the defined chamber also imparts to the subcaliber projectile an initial trajectory passing adjacent one portion of the oversized barrel wall for guiding the projectile along its intended path. Provision is made for the simultaneous firing of a plurality of subcaliber projectile from a single insert within the oversized chamber and barrel.

United States Franklin atet [54] SUBCALIBER ADAPTER FOR FIREARM [72] Inventor: Clarence W. Franklin, Cedar Tree Farm,

Milford, Calif. 96121 [22] Filed: May 5, 1969 [211 App]. No.: 821,616

[52] US. Cl. ..42/77, 102/41 [51] Int. Cl. ...F4lc 21/10, F41c 21/12 [58] Field olSearch ..42/77, 59; 102/41 [56] References Cited UNITED STATES PATENTS Feb. 8, 1972 FOREIGN PATENTS OR APPLICATIONS 316,732 8/1929 Great Britain ..42/77 Primary Examiner-Benajmin A. Borchelt Assistant ExaminerC. T. Jordan Attorney-Townsend and Townsend A chamber insert which defines a small caliber chamber through which an undersized or subcaliber projectile can be fired. The defined chamber is eccentric with respect to the larger chamber and barrel of the large caliber firearm so as to enable a center fire large caliber firearm to fire a smaller n'm fire subcaliber projectile. The eccentricity of the defined chamber also imparts to the subcaliber projectile an initial trajectory passing adjacent one portion of the oversized barrel wall for guiding the projectile along its intended path. Provision is made for the simultaneous firing of a plurality of subcaliber projectile from a single insert within the oversized chamber and barrel.

12 Claims, 10 Drawing Figures PATENIEUFEB emz 1640.013

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INVENTOR CLARENCE WILLARD FRANKLIN ATTORNEYS PATENTED FEB 8 I972 3,640,013

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ET BF 3 FIGJO INVENTOR. CLARENCE WILLARD FRANKLIN ATTORNEYS SUBCALIBER ADAPTER FOR FIREARM This disclosure relates to a subcaliber adapter permitting relatively large caliber firearms to fire projectiles of reduced size.

Subcaliber adapters or devices which permit relatively large caliber firearms to fire undersized cartridges are known. Typically, these devices include a chamber insert in combination with a barrel insert. The chamber insert fits the interior of the large caliber firearm chamber and defines a concentric and reduced subcaliber chamber for accommodating the subcaliber cartridge. The barrel insert fits the interior of the large caliber fireann barrel so as to be registered with the reduced chamber defined by the chamber insert. These two inserts in combination thus define a barrel and chamber of reduced dimension within the large caliber firearm through which the subcaliber projectile can be fired in the conventional manner.

The present subcaliber adapter dispenses with the need for a barrel insert. It has been found that a large caliber barrel can effectively confine the path of a subcaliber projectile to the desired bullet path provided that the projectile is fired with an initial trajectory passing adjacent one portion of the large caliber barrel wall. Moreover, by eccentrically mounting a rimfire cartridge of small caliber interior of an oversized chamber, many center fire firearms of relatively large caliber can be readily adapted to directly fire a subcaliber projectile without the necessity of altering or adapting the center fire mechanism of a large caliber center fire firearm.

An object of this invention is to provide a subcaliber adapter which fits entirely within the chamber of the large caliber firearm and does not require the necessity of a complementary barrel insert for the firing of the subcaliber projectile.

An advantage of this invention is that a revolver can be furnished with a new revolving chamber mechanism having subcaliber firing chambers defined therein. These chambers, located eccentrically with respect to the large caliber barrel, confine the path of the subcaliber projectile to an initial trajectory passing adjacent one portion of the large caliber barrel wall. This permits firing of a subcaliber projectile without modification of the barrel.

An additional advantage of this invention is that the revolving chamber mechanism of a revolver can be modified by the expedient of placing chamber inserts therein.

An additional object of this invention is to adapt rimfire cartridges, common in cartridges of relatively small caliber, to be fired directly by the center fire mechanisms common to firearms of relatively large caliber.

A still further object of this invention is to disclose a chamber insert which permits a conventional center fire mechanism of a relatively large caliber firearm to fire substantially simultaneously two or more subcaliber projectiles.

Other objects, features and advantages of the present invention will be more apparent after referring to the following specification and attached drawings in which:

FIG. 1 is a side elevation of a conventional revolver with the chamber and firing mechanism shown in section for illustrating the insertion of the subcaliber adapter of this invention;

FIG. 2 is an enlarged cross-sectional view of one of the chamber inserts or subcaliber adapters interior of the revolver of FIG. 1;

FIG. 3 is an end elevation section of the subcaliber adapter of FIG. 2;

FIG. 4 is a partial side elevation section of a center fire 20- gauge shotgun showing an inserted subcaliber adapter capable of permitting two smaller 22 cartridges to be fired substantially simultaneously;

FIG. 5 is an expanded side elevation section of the subcaliber adapter utilized in the shotgun of FIG. 4;

FIG. 6 is a side elevation of the subcaliber adapter of FIG. 5 along line 66 thereof;

FIG. 7 is an end elevation of a breechblock used with the subcaliber adapter;

FIG. 8 is a side elevation of the revolver of FIG. 1 illustrating the use of a revolving chamber mechanism defining subcaliber chambers according to the practice of this invention;

FIG. 9 is an end elevation of the revolving chamber along line 99 of FIG. 8; and

FIG. 10 is an end elevation of an alternate embodiment of the revolving chamber illustrated in FIG. 9.

With reference to FIGS. 1 through 3, the subcaliber adapter A of this invention is shown inserted interior of the chambers B of the rotating cylinder C of a revolver. This revolver has a center fire mechanism D. As is common in revolvers, rotating cylinder B revolves about an axis, indexing its chambers into registry with the revolver barrel before each shot is fired.

With specific reference to FIGS. 2 and 3, the subcaliber adapter inserted interior of the revolver is specifically illustrated. Adapter A comprises a solid metallic cylinder having an outside diameter 14 which enables it to be inserted interior of the chamber B of the rotating cylinder C of the revolver. At the end exposed to the center fire mechanism D, the insert is provided with an annular rim 15 which occupies the same spatial interval interior of chamber B as would be occupied by the rim a normally sized cartridge for the revolver. As is apparent, the subcaliber adapter has a length overall which occupies the entire axial extent of chamber B. Its rear surface 17 abuts the center fire mechanism D of the revolver and its front surface 18 extends to the full limit of the chamber extremity where it abuts the barrel when registered therewith.

Interior of subcaliber adapter A there is an eccentric bore 20 extending through the adapter from front surface 18 to rear surface 17. At the rear portion of bore 20, subcaliber chamber 22 is defined interior of the subcaliber adapter. Chamber 22 is cylindrical in shape and has an overall length which permits it to accommodate the casing of the subcaliber cartridge. At the rear portion of the subcaliber chamber 22, there is defined a subcaliber rim concavity 24. Concavity 24 is concentric with respect to eccentric bore 20 and extends peripherally about the eccentric bore so that it overlaps the centerline 25 of chamber B. From the forward portion of subcaliber chamber 22 to front surface 18 of the subcaliber adapter, there is preferably provided rifling 28 for imparting to the fired subcaliber projectile a spin about an axis parallel to its trajectory.

In operation, the subcaliber adapter is first inserted in the chamber B of the firearm. Likewise, a subcaliber cartridge 30 is inserted interior of subcaliber chamber 22. When the adapter and projectile are in place, the firearm can be fired. As is apparent, the center fire mechanism D of the firearm will impinge upon the rim 32 of subcaliber cartridge 30, resulting in firing of the firearm.

When fired, the subcaliber adapter in combination with the revolver will produce two effects upon the subcaliber projectile. First, rifling 28 between subcaliber chamber 22 and front surface 18 of subcaliber adapter A will impart to the projectile the traditional stabilizing spinning motion about an axis parallel to its trajectory. Secondly, once the projectile has left subcaliber adapter A it will pass adjacent to a portion of the wall of the oversize barrel of the revolver. Dependent upon the length of the barrel of the parent firearm, the projectile will be further guided in its trajectory along the barrel to a point where its accuracy substantially approaches that of the original firearm.

It will be noted that the subcaliber adapter is separated from the wall of the chamber B of the revolver by a small interval 35. Preferably, this interval 35 is precisely the same as that interval occupied by the casing of the regular sized cartridge for the firearm. With such an interval of separation, the initial trajectory of the projectile will pass contiguous to the oversized barrel of the revolver providing maximum stabilization and guidance of the projectile within the barrel of the large caliber firearm.

Subcaliber adapter A can be inserted with its eccentric bore 20 at virtually any angular position in the chamber D of the revolver. As rim 32 of subcaliber projectile 30 will always overlie centerline 25 of subcaliber adapter A, firing of the subcaliber projectile will always be possible.

It should be equally apparent that a center fire firearm, while preferred; is not necessary for the practice of this invention. By the expedient of rotating the subcaliber adapter within chamber B of the revolver to place the rim portion of the subcaliber cartridge in alignment with that portion of a rim fired firearm where impact occurs, this invention may be readily used with a large caliber revolver that is rim fired.

With reference to FIGS. 4 through 6, an embodiment of this invention is illustrated wherein a relatively large caliber center fire weapon such as a shotgun can be adapted to fire simultaneously two subcaliber projectiles.

Referring to FIG. 4, shotgun F having a center fire mechanism (3 is illustrated with a subcaliber adapter A inserted within a chamber H. As shown in FIG. 5, a subcaliber adapter A has a rear surface 117' and a front surface 18' with a length therebetween for occupying the entire chamber H of the shotgun. In overall diameter, the adapter A has a diameter 14 which enables it to fit interior of the chamber of the shotgun and an outside annular rim 15 which fits into the spatial interval defined by the shotgun shell rim suitable for use with the firearm.

Interiorly thereof, the subcaliber adapter A has two eccentric bores having corresponding subcaliber chambers 22 at the rearward portion thereof. EAch of the bores 20' has rifling 28' for imparting to the projectiles, a spin about an axis parallel to their trajectory.

At the rear portion of the lower subcaliber chamber 22', there is defined a subcaliber rim concavity 33. Rim concavity 38 is analogous to the rim concavity 24 of FIG. 2 in that it defines a concentric enlargement of the lower chamber 22' sufficient to accommodate the rim of the subcaliber projectile. When a projectile is contained within the chamber, as illustrated in FIG. 5, a portion of the rim is disposed to overlie the centerline 25 of the firearm chamber.

Similar to lower chamber 22, upper chamber 22' has a rimaccommodating concavity 39, which concavity accommodates the rim of the other subcaliber cartridge. Unlike the lower rim concavity 38, upper rim concavity 39 extends inwardly from the rear face 17' of the subcaliber adapter a distance twice the thickness of rim concavity 38. Upper subcaliber chamber 22' is also advanced with respect to the lower subcaliber chamber 22' by a distance equal to the rim thickness of the subcaliber cartridge so as to accommodate the upper subcaliber cartridge in an advanced position relative to the lower subcaliber cartridge 30'.

It will be noted that the rim of the lower cartridge overlies the rim of the upper cartridge at the centerline 25' of the adapter. This overlying permits center fire mechanism G of the shotgun F to impact both rims substantially simultaneously permitting substantially simultaneous discharge of both projectiles.

It will be appreciated that the subcaliber projectiles when fired will impel their respective casings rearwardly beyond surface 17'. Lower subcaliber projectile 30' will immediately abut the rear surface of chamber H of the shotgun and rearward reactive movement of the lower subcaliber cartridge casing will be prevented. Upper subcaliber cartridge 30, however, will not immediately abut the rear surface of chamber mechanism H and could cause jamming or wedging of the cartridge casing when fired, preventing their convenient removal from adapter A.

To prevent rearward movement of the upper subcaliber cartridge 30', there is inserted interior of upper rim concavity 38 immediately behind the subcaliber projectile 30, a breechblock 42. Block 42, rests directly upon the rearward surface of chamber H at one portion, abuts the rearward portion of the cartridge 30 at the other portion and fully occupies the spatial interval therebetween. This breechblock will prevent rearward movement of the upper cartridge 30' when firing occurs.

It will be appreciated, that the subcaliber adapters of this invention will work most efficiently when the subcaliber cartridge has a caliber approximating one-half the caliber of that of the large caliber firearm. This relationship will enable the rim of the subcaliber cartridge to overlie the centerline 25 and simultaneously will permit the projectile of the subcaliber cartridge to be discharged in a position where it is immediately adjacent a portion of the bore of the large caliber firearm.

The chamber insert here shown has been disclosed as fully occupying the chamber of the illustrated firearms. It is not necessary that this space be fully occupied so long as the walls of the designed subcaliber chamber are of sufficient thickness to withstand the forces generated in firing the subcaliber projectile.

It will be apparent that substantially any mechanism for defining a subcaliber chamber eccentrically disposed with respect to the bore of the large caliber firearm will be sufficient for the practice of this invention. In this case of a revolver, such a mechanism could well include an interchangeable rotating cylinder C for use with the invention. Such a rotating cylinder is illustrated in FIGS. 8 and 9.

Referring to FIGS. 8 and 9, the construction of such a cylinder C is illustrated. This cylinder defines a plurality of subcaliber chambers 50. These chambers are radially aligned with respect to the axis of cylinder rotation 5i so as to provide the subcaliber projectile with a trajectory which passes immediately adjacent to the bottom portion of the barrel wall of the oversized barrel in the firearm. Preferably the subcaliber cartridges 52 are each rimfired, have a caliber approximating half that of the large caliber firearm and are thus adapted to be fired by a center fire mechanism of the revolver.

Continual use of one portion of a large caliber firearm to fire subcaliber projectile in accordance with the practice of this invention could wear one portion of the barrel walls in relation to the other portions. Accordingly, it may be desired to randomly rotate the inserts as placed within the large caliber chamber so that successively fired projectiles will pass immediate different portions of the oversized barrel wall. Alternately, and as illustrated in FIG. 10, the subcaliber chambers when used in combination with a revolver can be given ditTering radial spacings from the axis of cylinder rotation 51 so that repeated fire of the six subcaliber projectiles illustrated in FIG. 10 will pass immediate six separate portions of the barrel wall of the oversized firearm.

What is claimed is:

1. A subcaliber adapter for a relatively large caliber firearm having a chamber and barrel adapted for said large caliber and a firing mechanism cooperating with said chamber, comprismg:

a conforming insert for occupying solely the chamber of said firearm; said insert defining a bore, eccentric to the axis of said chamber, between the firing mechanism and the barrel, having a concentric rear rim concavity, said bore being adapted for accommodating the firing of a subcaliber cartridge therein, wherein said subcaliber cartridge has a casing with a projecting rim at one end and a projectile;

wherein said bore with respect to the barrel of said large caliber firearm provides an initial trajectory for said projectile contiguous to and parallel to the wall of said large caliber barrel.

2. The invention of claim 1 and wherein said bore defines a barrel portion and a chamber portion said barrel portion includes rifling extending from said chamber portion to the barrel of said large caliber firearm.

3. The invention of claim 1 and wherein said bore defines a barrel portion and a chamber portion and said chamber portion is disposed for aligning a rimfire cartridge at the centerline of the large caliber chamber of said firearm.

4. The invention of claim 1 and wherein said insert includes more than one bore.

5. In combination: a firearm having a chamber communicating with a barrel of a first caliber, and a firing mechanism cooperating with said chamber;

an insert having outer boundaries for occupying said chamber;

said insert defining between said firing mechanism and said barrel a bore, eccentric with respect to said chamber,

having a rear rim concavity, said bore being adapted for accommodating the firing of a subcaliber cartridge therein, wherein said subcaliber cartridge has a casing with a projecting rim at one end and a projectile;

wherein said bore defines a barrel portion and a chamber portion, said barrel portion of said insert is aligned parallel to said chamber portion to provide the projectile of said cartridge with an initial trajectory, where it passes contiguous to and parallel to the wall of said large caliber barrel.

6. The invention of claim 5 and wherein said chamber portion is disposed for aligning a rimfire cartridge at the centerline of the large caliber chamber of said firearm.

7. The combination of claim 5 and wherein said insert defines two chamber portions and two barrel portions.

8. A subcaliber adapter for permitting a large caliber firearm to substantially simultaneously fire two cartridges of less than one-half the caliber of said large caliber firearm, said large caliber firearm having a large caliber barrel, a chamber and a center fire impact-firing mechanism, the center axis of said barrel being aligned with said center fire impact-firing mechanism; said adapter comprising:

a chamber insert having a length and width dimension sufficient to occupy said large caliber chamber; said chamber insert defining between said firing mechanism and said barrel paired bores eccentrically disposed with respect to said large caliber chamber; each bore having a chamber portion and a barrel portion for accommodating the firing of a subcaliber cartridge therein, said subcaliber cartridge having a casing with a projecting rim at one end and a projectile; each chamber portion disposed to locate each rim of each subcaliber cartridge in proximity to the axis of said chamber for substantially simultaneously impact firing of each cartridge by the single firing mechanism of said firearm.

9. The invention of claim 8 and wherein each barrel portion of the chamber insert is aligned with respect to the barrel of said firearm to provide the subcaliber projectile with an initial trajectory immediate the barrel wall of said firearm.

10. The invention of claim 8 and wherein one of said chamber portions is disposed with respect to the other of said chamber portions to overlie rims on said subcaliber cartridges at the central axis of the chamber of said firearm.

11. The invention of claim 8 and wherein one of said chamber portions is disposed ahead of the other chamber portion; and a breechblock is disposed between said one of said chamber portions and the firing mechanism of said firearm for preventing reactive rearward movement of said cartridge casing within one of said chamber portions.

12. The invention of claim 8 and wherein said firearm comprises a revolver having a removable rotating chamber. 

1. A subcaliber adapter for a relatively large caliber firearm having a chamber and barrel adapted for said large caliber and a firing mechanism cooperating with said chamber, comprising: a conforming insert for occupying solely the chamber of said firearm; said insert defining a bore, eccentric to the axis of said chamber, between the firing mechanism and the barrel, having a concentric rear rim concavity, said bore being adapted for accommodating the firing of a subcaliber cartridge therein, wherein said subcaliber cartridge has a casing with a projecting rim at one end and a projectile; wherein said bore with respect to the barrel of said large caliber firearm provides an initial trajectory for said projectile contiguous to and parallel to the wall of said large caliber barrel.
 2. The invention of claim 1 and wherein said bore defines a barrel portion and a chamber portion said barrel portion includes rifling extending from said chamber portion to the barrel of said large caliber firearm.
 3. The invention of claim 1 and wherein said bore defines a barrel portion and a chamber portion and said chamber portion is disposed for aligning a rimfire cartridge at the centerline of the large caliber chamber of said firearm.
 4. The invention of claim 1 and wherein said insert includes more than one bore.
 5. In combination: a firearm having a chamber communicating with a barrel of a first caliber, and a firing mechanism cooperating with said chamber; an insert having outer boundaries for occupying said chamber; said insert defining between said firing mechanism and said barrel a bore, eccentric with respect to said chamber, having a rear rim concavity, said bore being adapted for accommodating the firing of a subcaliber cartridge therein, wherein said subcaliber cartridge has a casing with a projecting rim at one end and a projectile; wherein said bore defines a barrel portion and a chamber portion, said barrel portion of said insert is aligned parallel to said chamber portion to provide the projectile of said cartridge with an initial trajectory, where it passes contiguous to and parallel to the wall of said large caliber barrel.
 6. The invention of claim 5 and wherein said chamber portion is disposed for aligning a rimfire cartridge at the centerline of the large caliber chamber of said firearm.
 7. The combination of claim 5 and wherein said insert defines two chamber portions and two barrel portions.
 8. A subcaliber adapter for permitting a large caliber firearm to substantially simultaneously fire two cartridges of less than one-half the caliber of said large caliber firearm, said large caliber firearm having a large caliber barrel, a chamber and a center fire impact-firing mechanism, the center axis of said barrel being aligned with said center fire impact-firing mechanism; said adapter comprising: a chamber insert having a length and width dimension sufficient to occupy said large caliber chamber; said chamber insert defining between said firing mechanism and said barrel paired bores eccentrically disposed with respect to said large caliber chamber; each bore having a chamber portion and a barrel portion for accommodating the firing of a subcaliber cartridge therein, said subcaliber cartridge having a casing with a projecting rim at one end and a projectile; each chamber portion disposed to locate each rim of each subcaliber cartridge in pRoximity to the axis of said chamber for substantially simultaneously impact firing of each cartridge by the single firing mechanism of said firearm.
 9. The invention of claim 8 and wherein each barrel portion of the chamber insert is aligned with respect to the barrel of said firearm to provide the subcaliber projectile with an initial trajectory immediate the barrel wall of said firearm.
 10. The invention of claim 8 and wherein one of said chamber portions is disposed with respect to the other of said chamber portions to overlie rims on said subcaliber cartridges at the central axis of the chamber of said firearm.
 11. The invention of claim 8 and wherein one of said chamber portions is disposed ahead of the other chamber portion; and a breechblock is disposed between said one of said chamber portions and the firing mechanism of said firearm for preventing reactive rearward movement of said cartridge casing within one of said chamber portions.
 12. The invention of claim 8 and wherein said firearm comprises a revolver having a removable rotating chamber. 